Typically, solid oxide fuel cells (SOFC) employ an electrolyte of ion-conductive solid oxide such as stabilized zirconia. The electrolyte is interposed between an anode and a cathode to form an electrolyte electrode assembly (MEA). The electrolyte electrode assembly is interposed between a pair of separators (bipolar plates). In use, generally, a predetermined number of the separators and the electrolyte electrode assemblies are stacked together to form a fuel cell stack.
As the structure of the fuel cell of this type, for example, the fuel cell separator structure disclosed in Japanese Laid-Open Patent Publication No. 63-266777 is known. In the separator structure, a corrugated plate formed by corrugating a metal flat plate by plastic forming is used as a separator. The corrugated plate has a plurality of cutouts for connection between both of front and back surfaces of the corrugated plate. The corrugated plate is provided at least on one side of a partition plate, and jointed to the partition plate such that the orientation of corrugation is aligned with the flow direction of the gas. According to the disclosure, in this manner, the manifold structure is simplified, and problems such as the flow failure or clogging, and non-uniform reactant gas concentration in the middle of the gas channel are eliminated.
In a fuel cell separator and a method of producing the fuel cell separator disclosed in International Publication No. WO 00/03446, a separator substrate 1 in the form of a flat plate 3, and a large number of projections 2 on the separator substrate 1 are provided, as shown in FIG. 30. The projections 2 have a circular truncated cone shape, and are arranged in rows and columns in a zigzag pattern, and spaced from each other at certain intervals. Gas channel differences are formed between the projections 2.
Further, in a fuel cell separator disclosed in Japanese Laid-Open Patent Publication No. 2005-293877, a metal substrate 1a is provided, as shown in FIG. 31. A plurality of metal covers 4a are formed on a front surface 2a of the metal substrate 1a, and a plurality of metal covers 5a are formed on a back surface 3a of the metal substrate 1a. The metal covers 4a and the metal covers 5a are spaced from each other, and aligned at equal intervals on the front surface 2a and the back surface 3a, or distributed at alternate positions on the front surface 2a and the back surface 3a. 
However, in Japanese Laid-Open Patent Publication No. 63-266777, since the cutouts are formed in the corrugated plate, the contact area between the separator and the MEA tends to be small. Therefore, the reactant gas tends to flow through without being consumed, and the power generation efficiency may be lowered undesirably. Further, the strength of the separator itself is lowered. Warpage or the like occurs easily in the separator, and the separator is deformed.
Further, in International Publication No. WO 00/03446, though the projections 2 are arranged in a zigzag pattern on the separator substrate 1, due to the structure of the fuel cell as a whole, it may not be possible to effectively increase the contract area with the MEA. Thus, improvement in the power generation efficiency cannot be achieved. Further, it may not be possible to sufficiently suppress warpage of the separator and deformation of the separator.
Further, in Japanese Laid-Open Patent Publication No. 2005-293877, the metal covers 4a are provided in a matrix pattern on the front surface 2a of the metal substrate 1a, and the metal covers 5a are provided in a matrix pattern on the back surface 3a of the metal substrate 1a. Therefore, it is difficult to effectively increase the contact area with the MEA. Further, warpage and deformation of the separator cannot be suppressed, and the reactant gas may flow through without being consumed.